There has been conventionally used a construction vehicle tire having a so-called lug pattern, wherein a number of lug grooves are arranged at a predetermined distance from each other. In such a construction vehicle tire, generally, a tread rubber having a high wear resistance is used in order to provide an improved wear resistance of the tire, and the tread volume is increased to increase the tread gauge and decrease the negative ratio, thereby to provide an improved stiffness at the land region.
However, when these measures are taken for improving the wear resistance of the tire, the temperature of the tread portion tends to further rise due to degraded heat generation property and increased heat generation value particularly upon rolling of the tire under a loaded condition. This sort of temperature rise in the tread portion is undesired from the viewpoint of preventing heat separation, etc., at the tread portion.
The tendency of the temperature rise is noticeable in particular at a land region with a small heat radiation area, when the land region is defined between two straight lines connecting the terminal ends of the lug grooves substantially in the tire circumferential direction and extending along the circumference of the tire.
As a countermeasure for coping with such a problem, there has been recently developed a technology that serves to minimize the decrease in the tread volume, minimize the lowering of the stiffness at the land region, and thereby provide an increased heat radiation area. This technology is featured by the provision of shallow circumferential grooves having a depth that is not larger than 25% of the depth of the lug groove, and a width that is within a range of approximately from 30 mm to 50 mm (refer, for example, to Patent Documents 1 and 2 identified below).                Patent Document 1: JP 2001-213120 A        Patent Document 2: JP 2000-233610 A        
However, with the recent trend toward a large scale construction vehicle, and corresponding requirement for construction vehicle tires with increased tire size, low aspect ratio and increased duty load, there is even more significant tendency of the degraded heat generation property and the enhanced temperature rise at the tread portion. Thus, suppression of the temperature rise at the tire center portion is still a highly important task.